The lead singer of Germany's best-selling girl band wept today as she apologised to her former sexual partners for failing to disclose to them that she was carrying the HIV virus.

Nadja Benaissa, 28, of the group No Angels, told the court in Darmstadt that she had failed to tell her partners about her condition. "In those days I was careless," she said, adding: "I'm sorry from the bottom of my heart."

She is appearing before a juvenile court because the alleged crimes began when she was just 17, the age at which she discovered she was HIV positive.

The singer, who is accused of grievous bodily harm and attempted aggravated assault, said she had not meant to cause any of the men injury, having been advised that it was highly unlikely that she would transfer the virus to anyone with whom she had sex.

"I never wanted this to happen to any one of my partners," she said.

In a statement by the singer, read to court by her lawyer, Oliver Wallasch, she added: "I'd been told the likelihood of infecting someone or that I would develop the illness [Aids] was more or less zero. For that reason I kept the news even from my close group of friends [as] I didn't want my daughter to be stigmatised. I told the band members because I trusted them but I never made it public because I feared that it would mean the end of the band."

She added that while she could not recall "all the details of my private life over the last decade", it was "possible" that all the accusations against her were true.

Benaissa is accused of having had sex with three men around five times between 2000 and 2004 without informing them of her HIV status. One of the men subsequently became infected with HIV.

Giving evidence to the court, the unidentified man said: "We had sex between five and seven times, about three of those were unprotected." He said he had only found out that Nadja was HIV positive after being told by her aunt. "I went to the doctor, and after a few hours he called me and said I should go to see him. It was then I knew I was positive," he said.

Turning to the accused, the 34-year-old man added: "You have unleashed a lot of misery into the world."

The five-day trial is due to hear from Professor Josef Eberle of Ludwig Maximilian University in Munich, who is expected to testify that the man may have been infected by someone else.

Benaissa, whose HIV status was discovered a decade ago during a pregnancy test, was arrested in April 2009 just before No Angels were due to appear on stage at a Frankfurt nightclub, after one of her sexual partners pressed charges against her. She was handcuffed by plainclothes police and driven away in front of fans, before being held in custody for 10 days.

Campaigners for the rights of victims of HIV and Aids were highly critical of the public manner in which the arrest was made, calling it a "modern witch-hunt", and have accused prosecutors of a grave breach of privacy after they made public the fact that Benaissa had HIV.

Under German law the crime of failing to disclose you have HIV to someone before having sex with them carries a prison sentence of between six months and 10 years. If the victim dies as a result of infection the sentence can extend to life imprisonment.

Benaissa's is the first trial of its kind in Germany in which a celebrity is in the dock.

Following the disclosure of her illness the singer has often talked publicly about it, including in a prominent speech to the Berlin Aids Gala last November, in which she said: "I thought my life was destroyed, as well as that of my nine-year old, infection-free daughter."

But she has stressed that thanks to modern medicine "I am a completely healthy person, even if I'm HIV positive. I have a perfectly normal life expectancy."

No Angels, an all-girl band with four members, was discovered 10 years ago during a TV talent show when they beat 4,500 other hopefuls for the top prize. They went on to become Germany's most successful female band, often compared to Girls Aloud. Between 2000 and 2003 they sold 5 million records, including three No 1 albums and four No 1 singles, among them their most famous hit, Daylight in Your Eyes.

The band broke up but reunited to take part in the Eurovision song contest in 2008, in which they came 23rd. They released a new album last summer.

Witnesses in the trial, which has attracted scores of No Angels fans, are expected to include Benaissa's fellow band members, Sandy Mölling, Jessica Wahls, and Lucy Diakovska. A verdict is due on 26 August.

The band's manager, Khalid Schröder, refused to comment on rumours that Benaissa is no longer a member of the group. "We are sure to issue a statement after the close of the trial," he said.